MA, Lin, Geological Sciences, University of Texas at El Paso, 500 W. University Ave, El Paso, TX 79968, lma@utep.edu, ENGLE, Mark A., U.S. Geological Survey, UTEP Dept. of Geological Sciences, El Paso, TX 79968, RUPPERT, Leslie, Eert, U.S. Geological Survey, 956 National Center, 12201 Sunrise Valley Dr, Reston, VA 20192, and GEBOY, Nicholas J., U.S. Geological Survey, 956 National Center, Reston, VA 20192